1. Field of the Invention
The invention relates to movement vector detecting method/apparatus for detecting a movement vector of an object between frames and also relates to encoding method/apparatus using such vector detecting method/apparatus.
2. Related Background Art
What is called a block matching type is known as a movement vector detecting system.
According to the movement vector detecting system of the block matching type, one block is formed by extracting pixels of (8.times.8), (16.times.16), or the like between the previous frame and the present frame, a matching is performed for every block of data, and a movement vector is assigned to each block of the present frame.
A fundamental idea of the movement vector detecting system will now be described in detail hereinbelow.
A block in which the pixel position at the left upper corner on the present frame is set to (i, j) and which is constructed by m pixels in the lateral direction and n pixels in the vertical direction assumes a vector value B.sub.ij (m, n). A block at the same position on the previous frame as that of the block B.sub.ij (m, n) assumes a vector value P.sub.ij (m, n). In this instance, an evaluation function of an error between B and P is defined as follows: ##EQU1##
The movement vector is defined by using deviations x and y from i and j such as to obtain the minimum value of f when x and y are changed within a range from .+-.0 to s (s is a parameter of a retrieving area).
Generally, a color moving image is constructed in a form such that one frame is divided into luminance data (Y) and color difference data (C.sub.r, C.sub.b, etc.). The luminance data (Y) including much structure information is used to retrieve the movement vector. There is also known a method of retrieving a new vector by using the block just before or the vector obtained in the peripheral block as a center, a method of estimating a movement of the whole picture plane by obtaining a correlation between the vectors which are generated from the individual blocks and the block positions, or the like.
However, an actual meaning image (not a mere set of RGB luminance data but an image having information as what is ordinarily called a picture, such as person, scenery, test pattern, or the like) contains many colors and a set of points of the same hue inherently mean one collected object.
In the usual matching by the blocks using the luminance data, although an error value on calculation can be locally minimized, it is difficult to detect the same object in the image.
Therefore, when a movement of the whole picture plane is obtained from the vectors or when the vectors generated in the previous block or the peripheral blocks which have been processed are, used to retrieve the vector in the present block, then on the contrary a large error is caused.
According to the block matching system, since the an amount of calculation is very large, an averly wide range cannot be retrieved. Therefore, when a movement of an object is large, the movement width of the block can easily exceed the retrieval range, and the matching cannot be effectively executed.